1. Field of the Invention
The present invention relates to control over the image formation part of an image forming apparatus, particularly control based on a change in status or condition of the image formation part.
2. Description of the Related Art
A variety of output apparatuses have conventionally been used for output by a computer, including image forming apparatuses, such as an electrophotographic printer (hereunder referred to as a "laser beam printer"), bubble jet printers, and the like.
FIG. 16 is a block diagram illustrating the configuration of a printer controller portion of a conventional image forming apparatus, the configuration of a printer engine portion thereof and an interface between both of these portions. In this case, the illustrated apparatus is as a laser beam printer including a printer controller portion 603 and a printer engine portion 605.
The printer engine portion 605 comprises an engine control portion 650, a paper (or sheet) size detecting portion 651, a presence-of-paper detecting portion 652, a presence-of-option detecting portion 653, a paper conveyance control portion 654, an optical system control portion 655, a fixing-device temperature control portion 656, an option control portion 657 and a sensor input portion 658.
The printer controller 603 is operative to communicate with external equipment (to be described later) over interface 606 (such as an interface to a centronics or IEEE-1284 communication port), to receive image data therefrom and further develop the received image data to printable information. Moreover, the printer controller portion 603 is operative to exchange various kinds of signals with the engine control portion 650 and performs a serial communication therewith. The engine control portion 650 controls each of the units or parts of the printer engine portion 605 through the exchange of the signals and the serial communication.
The paper size detecting portion 651 is operative to detect the paper size of paper stored in a paper (or sheet) cassette (to be described later) and to further transmit detection information to the engine control portion 650. The presence-of-paper detecting portion 652 is operative to detect whether or not sheets of paper are stored in the paper cassette, and to further transmit detection information to the engine control portion 650. The presence-of-paper detecting portion 652 is also operative to detect the presence of paper at each of a manual paper feed opening or entrance (not shown), an option-cassette paper feed opening (not shown) or an envelope-feeder opening (not shown).
The paper conveyance control portion 654 is operative to perform a control operation concerning the conveyance of paper. The optical system control portion 655 is operative to perform control operations concerning a scanner motor (not shown) and an optical system using laser light. The fixing-device temperature control portion 656 is operative to control the temperature of a fixing device (not shown) and detect an abnormality therein. The option control portion 657 is operative to send action directives to the option cassette (not shown) and the envelope feeder (not shown). The sensor input portion 658 is operative to detect the presence of paper in a conveyance path at the time of performing an operation of a resist shutter, a paper discharging operation, a both-side (or duplex) print operation and a paper reversing operation.
The interface (hereunder referred to as a "video interface") between the engine control portion 650 and the printer controller portion 603 will be described hereinbelow corresponding to each of the following signals exchanged therebetween.
First, /CPRDY signal 670 indicates that the printer controller portion 603 is in a state in which this portion 603 can communicate with the engine control portion 650, and is transmitted from the printer controller portion 603 to the engine control portion 650. Next, /PPRDY signal 671 indicates that the printer controller portion 603 is in a standby state in which the engine control portion 650 is ready for communicating with the printer controller portion 603, and is transmitted from the engine control portion 650 to the printer controller portion 603.
Further, /RDY signal 672 indicates a standby state of the engine control portion 650, and is transmitted from the engine control portion 650 to the printer controller portion 603. If the engine control portion 650 is ready for printing, this signal represents a value of "TRUE". In the case that the engine control portion 650 is not ready for printing, the /RDY signal 672 has a value of "FALSE". Further, /PRNT signal 673 indicates a request for printing issued from the printer controller portion 603 to the engine control portion 650, and is transmitted from the printer controller portion 603 to the engine control portion 650.
Furthermore, /VSREQ signal 674 indicates a request for a vertical synchronization (or synchronizing) signal issued from the engine control portion 650 to the printer controller portion 603, and is transmitted from the engine control portion 650 to the printer controller portion 603. Additionally, /VSYNC signal 675 is a vertical synchronization signal outputted by the printer controller portion 603 to the engine control portion 650 and is transmitted from the printer controller portion 603 to the engine control portion 650. /BD signal 676 is a horizontal synchronization signal and is transmitted from the engine control portion 650 to the printer controller portion 603.
Further, /SCLK signal 678 is a synchronous clock signal for serial communication and is transmitted from the printer controller portion 603 to the engine control portion 650. Moreover, /CMD signal 679 is a command sent from the printer controller portion 603 to the engine control portion 650, and is transmitted from the printer controller portion 603 to the engine control portion 650. Furthermore, /CBSY signal 680 is a strobe signal for outputting a command and is transmitted from the printer controller portion 603 to the engine control portion 650.
In addition, /STS signal 681 is the status of the inside of the printer engine portion 605 and is transmitted from the engine control portion 650 to the printer controller portion 603 as an output thereof in response to a command from the printer controller portion 603. Further, /SBSY signal 682 indicates status output period and is transmitted from the engine control portion 650 to the printer controller portion 603.
In the case of such a conventional image forming apparatus, the printer controller portion receives information such as a paper conveyance condition, errors due to a paper jam or the like, and warnings of a reduction in the remaining quantity of toner, from the engine control portion by performing a serial communication prescribed by the aforementioned video interface (more particularly, a communication to be performed by using the /SCLK signal 678, the /CMD signal 679, the /CBSY signal 680, the /STS signal 681 and the /SBSY signal 682 of FIG. 16), and performs a predetermined operation corresponding to the received information.
Further, the aforementioned video interface has a signal line (corresponding to the /RDY signal 672) dedicated to indicate a printable state or an unprintable state. The printer controller portion does not perform an operation of recognizing the state (for example, a jam state) of the printer engine portion until this /RDY signal has a value of "FALSE" representing the unprintable state. In contrast, in the normal case, namely, in the case that the /RDY signal 672 has a value of "TRUE" representing the printable state, the printer controller portion is adapted to keep track only of the warning of a reduction in the remaining quantity of toner, which does not relate to whether or not a printing operation can be performed, by monitoring polling signals.
Recently, in connection with an image forming apparatus that has a plurality of paper feed portions, such as a plurality of paper (or sheet) cassettes or a plurality of multiple purpose (or use) trays, it has been considered to provide the apparatus what is called an automatic paper feed selection function, namely, a function to recognize the (size of) paper included in the plurality of paper feed portions, searching the plurality of paper feed portions for paper of an indicated size, and selecting a paper feed portion, in which sheets of paper of the size matched with the designated size are included, from the plurality of paper feed portions as a paper feed portion to be actually used for feeding paper.
Moreover, there has been already known another image forming apparatus that has a power-thrifty standby mode in which unnecessary consumption of power is suppressed in an idle state.
However, in the case of the aforementioned image forming apparatuses, it is necessary to monitor or otherwise keep track of states (for example, a paper jam state and a state in which a door is opened), which are not reflected by the /RDY signal 672 in the printer engine portion, namely, the image forming portion. This involves periodic serial communications regardless of changes in such states, and consequently without regard to the need for such serial communication. Especially, in the case of employing the automatic paper feed selection functions, a serial communication for selecting one of the paper feed portions is needed every printing operation. Thus, conventional image forming apparatuses have problems in that there is processing overhead to perform monitoring operations, and this processing overhead becomes a factor which impedes high-speed communications and puts an excessive burden on the control portion. To reduce this overhead, it has been considered to provide the apparatus with a signal line dedicated to each different status of the image forming portion, but this idea is not practical as to the cost thereof.
Therefore, the aforementioned conventional image forming apparatuses have an additional problem in that it is difficult to prevent reduced speed of communications caused by the increase in burden put on the control portion from its monitoring operations, while at the same time reducing the cost thereof.